Method and apparatus for forming double walled containers



Ail g 1968 R. F. WESTCOTT 3,396,430

METHOD AND APPARATUS FOR FORMING DOUBLE WALLED CONTAINERS Filed May 15, 1967 14 39 42 34?FQ48Z22 52 18 I INVENTOR.

Ao be/'/ P. Wes/co/f HTTORNE Y United States Patent 3,396,430 METHOD AND APPARATUS FOR FORMING DOUBLE WALLED CONTAINERS Robert F. Westcott, Findlay, Ohio, assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Continuation-impart of application Ser. No. 306,249, Sept. 3, 1963. This application May 15, 1967, Ser. No. 638,241

5 Claims. (Cl. 18-19) ABSTRACT OF THE DISCLOSURE A method and apparatus for forming double walled containers, such as meat trays and the like, wherein a plug and a mating cavity die engage a pair of preheated plastic sheets, the plug and die engaging a sheet from the opposite direction and progressing toward one another, wherein vacuum and air pressure are employed to keep the sheets separate in the double walled area. Optionally included are ribs for forming reinforcing indentations in one of the walls when this may be desired.

This application is a continuation'in-part of copending application Ser. No. 306,249, filed Sept. 3, 1963 now abandoned.

Description of the invention This invention relates generally to forming of double articles and, more particularly, relates to apparatus for providing double walled trays formed from two sheets of a plastic material.

Accordingly, it is an object of the present invention to provide a novel apparatus for forming double walled contatiners from plastic materials.

Another object of the present invention is to provide a novel apparatus for forming a double bottom container from two sheets of plastic in a single operation.

Still another object of the present invention is to provide a novel apparatus palticularly adapted for forming double walled tray-type containers of plastic foam.

Briefly then, the present invention describes an apparatus for forming double walled containers wherein a plug and a mating cavity die engage a pair of preheated plastic sheets, the plug and die engaging a sheet from the opposite direction and progressing toward one another, wherein vacuum and air pressure are employed to keep the sheets separate in the double walled area. Optionally included are ribs for forming reinforcing indentations in one of the walls when this may be desired.

Yet additional objects and advantages of the present invention, and its numerous cognate benefits and features are even more apparent and manifest in and by the ensuring description and specification taken in conjunction with the accompanying drawing in which, wheresoever possible, like characters of reference designate corresponding material and parts throughout the several views thereof, in which:

FIGURE 1 is a cross-sectional view of apparatus used in forming a double bottom tray in its opened preforming position; and

FIGURE 2 is a view similar to FIGURE 1 only showing the apparatus in its closed forming position.

Apparatus includes a plug 12 and a mating cavity die 14, each preferably formed of aluminum or other suitable material. The plug and die are movable toward and away from one another, as illustrated in FIGS. 1 and 2, by way of frame member 16 and 18, respectively, driven by motors (not shown). A plurality of passageways 20 are formed through plug 12, and similar passage- 'ice ways 22 are formed through die 14, the latter being connected to a passage 24 leading to a vacuum chamber 26.

Located in the top of plug 12 is a block 28, preferably formed of an insulating material such as polytetrafluoroethylene or the like. Block 28 carries a needle 30 which extends beyond the bottom or base portion 33 of plug 12, this needle being hollow so as to provide an air passageway 32. Also contained within block 28 are heated coil terminals 34 connected with metallic tip 36 of needle 30 for providing the tip with sufiicient heat to provide an opening, i.e. by burning away, piercing, puncturing, etc., through one layer of a plastic sheet when engaged therewith. For example, two layers 40 and 42, clamped together (clamps not shown) at their outer ends 39 are shown in FIGURE 1 as being located between plug 12 and die 14, layer 40 being the upper layer which is to be pierced by needle 30. Preferably, layers 40 and 42 are spaced from one another, except at their outer ends 49, by tubing 41, which can be a polytetrafluoroethylene coated steel tubing. Small holes (not shown) can be spaced along tubes 30, through which air can be blown to keep the sheets separated when hot.

Die 14 is also illustrated as including projections 46 extending from its base portion 35 and which can be employed to form ribs in the bottom of a container formed by apparatus 10. This will provide integral reinforcement of layers 40 and 42 against one another when the container is placed in use. Pointed heads 48 can also be provided. These would extend beyond the bottom or base portion 33 of plug 12 a distance greater than the thickness of sheet 40 when it is desired to provide passages 37 whereby excess fluids contained in a formed container can fiow into the space or reservoir 39 between layers 40 and 42.

The process of the present invention comprises the preheating of two sheets of plastic film or foam, i.e. layers 40 and 42, preferably formed of a thermoplastic material such as polystyrene or polyethylene. The heated sheets are transferred to the apparatus 10 as illustrated in its open preforming position in FIGURE 1.

In its operation, plug 12 of apparatus 10 moves downward until it strikes upper sheet 40 and preferably traps this sheet tightly against the plugs surface by use of a vacuum drawn through passageways 20. The tip 36 of needle 30 provides a small hole in the layer 40 as the plug strikes the sheet.

Die 14 closes tightly against the plug 12 and draws bottom layer or sheet 42 down into its configuration by pulling of a vacuum through passageways 22 and 24, as illustrated in FIGURE 2. Preferably plug 12 and die 14 move together simultaneously with the opening by needle 30 being formed during this movement. The main reason it is desirable to move die 14, as well as plug 12, is to provide for later ease of ejection of the formed container upon withdrawal of die 14.

The bringing together of plug 12 and die 14 forms a welding of layers 40 and 42 about their adjacent side wall peripheries when the spacing is properly dimensioned so as to be, for example, only slightly less than that of the thickness of the two layers combined.

Air is introduced between layers 40 and 42, through the hole 32 of the needle, thus filling the cavity between the two layers of plastic sheet with a ballooning or billowing effect. This blowing air is preferably metered to a given volume approximating atomspheric pressure. If ribs 46 are employed, layer 42 will, of course, form thereabout. If the ribs 42 are of adequate height, then the top of layer 42 will be heat sealed to the bottom of layer 40 along lines or seams identified by reference character 52.

Thence the plug and die are opened and the formed container is ejected and sent to a trimming station. However, if desired, the container may be trimmed in the mold before the mold is opened by adaptations of appanatus 10 not here shown or considered essential to the present invention.

It is to be understood that the above process can be used for many types of containers. For example, its teaching would only have to be slightly modified to allow the forming of hollow side walls as well as bottom walls, if desired. Also, if the hole formed in layer 40 by needle 30 were to be sealed, excellent insulating properties between layers 40 and 42 could be obtained. Otherwise, additional holes can be provided in layer 40-, by heads 48, to provide a container with drain-off facilities.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the'art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

. Accordingly, what is claimed as new is:

1. An apparatus for forming double Walled containers from a pair of thermoplastic sheets, said apparatus comprising a plug, a cavity die, means connected with said plug and die rendering at least one of them movable toward the other, said plug being matable with said die and when in a closed position defining a space between base portions of each the distance therebetween being greater than the combined thickness of said sheets and defining a space between at least peripheral portions of adjacent sides of said plug and die the distance therebetween being substantially no greater than the combined thickness 4 7 V I 1' of said sheets, a hollow needle having a tipproject in g below the base portion of said plug a distance greater than that of the thickness of the sheet to be engaged by said plug but less than that necessary to penetrate the other of said sheets, and a source for introducing fi-uid under pressure through said hollow needle.

2. The apparatus of claim 1 wherein said hollow needle is provided with means to heat it to a temperature sufficient to burn through said one of saidsheet s. V s

3. The apparatus of claim 2 wherein a vacuurni port means extends through each of said plug and die openings into said space. Y l

4. The apparatus of claim 3 wherein ribs are formed integral with said base portion and extend into said space. 5. The apparatus of claim .4 wherein said ribs extend above the top surface of said die a distance less than said first mentioned distance, and apluralitybf" projections extend from the bottom surface of said plug at least a distance greater than the thickness of at least one of said sheets. I References Cited UNITED STATES PATENTS 1,387,616 8/1921 Roberts. 2,810,160 10/ 1957 Bottleman. 3,242,245 3/1966 Greig et al. 3,250,660 5/ 1966 Greig et al. 3,308,213 3/1967 Carrigan et al.

WILLIAM J. STEPHENSON, Primary Examiner. 

